The present invention relates to the support platform for a raster output scanning (ROS) system and, more particularly, to a cast honeycomb structure with integral damping to support and reduce vibrations to the ROS system.
Printing systems utilizing a ROS to form images on a photoreceptor surface are well known in the art. Conventionally, the ROS includes a laser for generating a coherent beam of radiation; a modulator for modulating the laser beam in accordance with an input signal; and a multi-faceted polygon mirror for scanning the modulated laser beam line by line across the surface of a photosensitive medium to form a latent image. Also included in the ROS are various optical components to collimate, expand, focus, and align the modulated scanning beam. These optical components are fixedly mounted within a housing frame, which is positioned within a printer machine frame, so that the modulated and shaped scanning beam emerging from a window in the housing is directed along a scan line on the surface of the photosensitive medium. The scan lines will be formed in parallel in a raster pattern across the surface of the photosensitive medium.
As shown in the prior art printing system of FIG. 1, the raster output scanner 10 is positioned in the ROS housing 12 to emit a scanning beam to the exterior photosensitive medium (a photoreceptor) 14.
The raster output scanning system 10 utilizes a laser diode light source 16 to emit a modulated coherent light beam 18. The light beam 18 is collimated by a multi-element optical collimator 20. Mirrors 22 and 24 fold and redirect the light beam 18 within the housing 12. A cross-scan cylindrical lens 26 focuses the light beam 18 in the sagittal or cross scan plane onto a facet 28 of the multi-faceted polygon mirror 30 while maintaining the collimation of the scan portion of the beam. The light beam 18 thus forms a line on the facet 28. Mirror 32 folds and redirects the light beam 18 from the cylindrical lens 26 to the facet 28.
The light beam 18 is reflected from the facet 28. A motor 34 rotates the facet 28 so that the light beam will scan across the photoreceptor 14.
The light beam 18, after reflection from the facet 28, is still collimated in the scan plane and is now diverging in the cross-scan plane. The beam 18 then passes through an f-theta scan lens 36 consisting of a negative plano-spherical lens 38, a positive plano-spherical lens 40 and a cross-scan cylindrical lens 42. This f-theta scan lens configuration converges the beam 18 in the scan axis.
After passing through the f-theta scan lens 36, the light beam 18 is then reflected off a cylindrical wobble correction mirror 44. The mirror 44 is positive and cylindrical in the cross-scan plane and flat in the scan plane. Thus, the wobble mirror converges the previously diverging cross-scan portion of the light beam 18 but allows the converging cross-scan portion of the light beam 18 focused by the f-theta lens 36 to pass through unaffected. The reflected beam 18 is focussed onto a scan line 46 on the photoreceptor 14.
The housing provides physical support for the optical components of the raster output scanning system and positions the scanning system relative to the photosensitive medium. The scanning beam must be properly aligned and focused on the photosensitive medium.
A raster output scanner is usually implemented with the rotating polygon mirror as part of a motor polygon assembly. The motor polygon assembly includes not only the polygon, but also a drive motor, bearings, shafts, mounts, and, possibly, a speed control circuit for the motor. In practice, the motor polygon assembly is usually the largest and heaviest component of the raster output scanner to be supported by the housing. The lens and stationary mirrors of the raster output scanner are smaller and lightweight in comparison.
The laser, polygon mirror and motor, and the lens and mirrors of the ROS are either attached directly to the housing or, more typically, mounted on brackets which are attached directly to the housing. The housing is usually metal or a high density rigid plastic or a reinforced polycarbonate material.
Vibration always poses a problem to the positioning and focusing of the scanning beam. External vibrations can come from any number of sources including the photosensitive medium itself if the medium is a rotating photoreceptor belt. The major source of internal vibration is the rotating polygon mirror and motor.
The high speed rotation of the polygon mirror can cause vibrations which misalign or misfocus the other optical components of the raster scanner, particularly the lightweight lens and mirrors. Contrarily, the rotating polygon mirror itself is sensitive to vibrations which can misfocus or misalign the scanning beam reflected from the revolving facets.
While positioning and focusing the raster output scanner relative to the photoreceptor is difficult in black only printing, with color printing using multiple raster output scanners, proper positioning and proper focusing of the raster output scanners relative to the photoreceptor or photoreceptors becomes even more difficult.
Vibration dampers are well known. External compression springs are used to support and isolate a ROS from vibration in U.S. Pat. No. 5,760,818, commonly assigned as the present application and herein incorporated by reference. Other types of vibration dampers include attaching the ROS optical component mounts inside the housing to elastomeric materials that absorb vibration energy.
The housing for a raster optical scanner must provide a very rigid base for the ROS for meeting the extreme scanning beam position stability requirements of high performance imagers. In addition, it would be advantageous for the housing to be able to damp certain vibration modes.
It is an object of the present invention to provide a rigid housing to support the optical components of the raster output scanning system and position the scanning system relative to the photosensitive medium and to provide a housing that damps internal and external vibration modes.
It is another object of the present invention to provide a honeycomb structure housing with integral damping layers to support and reduce vibrations to the ROS system.
According to the present invention, a honeycomb structure is formed integral with a raster output scanning system housing. A constrained layer damper is bonded to the honeycomb structure and the raster output scanning system is mounted on the constrained layer damper. The honeycomb structure and constrained layer damper provide support and reduce vibrations to the raster output scanning system. The cells of the honeycomb structure can be irregular in height, thickness, density or shape to further support and damp vibrations.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.